If this were me, I would answer no since your family members do not have their B2's in hand right now. If they do get B2's prior to your K1 interview, you can discuss that with the consulate officer conducting your interview and change it is needed.
Be very careful with any engagement parties, or religious engagement ceremonies that can look like some form of wedding when you are applying for a K1. In general you should be fine, but make sure it looks like an engagement ceremony, and not a wedding.
Good Luck!